This invention relates to the field of constantvoltage, power supply circuits and particularly, to power supply circuits using silicon controlled rectifiers (SCRs).
In general, power supply systems designed for use in point of sale terminals, like electronic cash registers for example, typically used a traditional half or full-wave bridge circuit driving a storage/regulator type system. While this system has worked well and is still widely used, it has severe disadvantages in terms of cost, heat dissipation problems, size of components required, sensitivity to line voltage variation, and sensitivity to and efficiency as a result of load current variations.
The circuit of this invention includes a capacitor which is used as an energy storage device. Special switching means are included within the circuit to minimize the power consumption within the circuit, to minimize heat dissipation, and consequently reduce the cost and size of the heat sinks required.
In general, the circuit of this invention uses a silicon controlled rectifier (SCR) as the rectifier and controls it in such a way as to allow certain voltage conditions to be maintained across a capacitor which is used as an energy storage device. This capacitor is rapidly charged to some upper voltage limit V.sub.1 and is then allowed to discharge linearly (by a load) to a lower limit V.sub.2. It is then charged again to V.sub.1 and the cycle is repeated. The values of V.sub.1 and the capacitor are chosen so as to require recharging only at large intervals (over a period of several input A.C. cycles). Current is drawn through the SCR only during the charging from V.sub.2 to V.sub.1 (less than 1/2 cycle A.C.). Special switching means are included within the circuit to minimize power dissipation therein. The output of the capacitor may then be fed to a battery charging circuit, or to a subsequent terminal voltage regulator, or it may be used directly as a power supply source.
Some representative prior art power supply circuits are shown in the following U.S. Pat. Nos.: 3,781,632; 3,939,394; 3,959,716; 3,969,665; 3,987,354; and 3,987,356.
Of these patents, U.S. Pat. No. 3,939,394 discloses a power supply circuit using a silicon controlled rectifier for charging a capacitor; however, this circuit does not show the special switching means included in the circuit of the present invention so as to minimize power consumption therein.